The so-called Short Message Service (SMS) is a Teleservice specified in some modern cellular communications systems, for example IS-136, for enabling a user to send messages to, and receive text messages from, the communications network. The SMS attempts to deliver a message to a mobile station (MS) whenever the mobile station is registered to the network, even when the mobile station is engaged in a voice or data call. The mobile station may roam throughout the network and still be capable of sending and receiving messages. As presently specified in IS-136.1, a mobile station configured for SMS provides methods for the user to receive, read, clear, send, and save messages.
The IS-136 specification presently enables both mobile station terminated (network to mobile station) and mobile station originated (mobile station to network) SMS. The SMS Point-to-Point, Paging and Access Response Channel (SPACH) is specified for use in the mobile station terminated SMS mode. As is specified in IS-136.1 Rev. A, Mar. 21, 1996, Section 7.1.1.2.1 and Section 7.1.2.2, a SMS Submit message is also defined for sending a SMS message from the mobile station. The SMS Submit message is specified to be sent to the network, more particularly to the Base Station/Mobile Switching Center/Interworking Function (BMI), in an R-DATA message. The R-DATA message is sent on a reverse (i.e., MS.fwdarw.BMI) digital control channel.
It can be appreciated that the use of the reverse digital control channel to send the mobile station originated SMS messages has the disadvantage of consuming a valuable system resource that could otherwise be used to convey signalling information for, by example, mobile station registration and call origination purposes. Typically, there are significantly fewer digital control channels assigned in a wireless communications system than there are traffic (e.g., voice and/or data) channels. While the use of the digital control channel may not be especially disadvantageous for one mobile station transmitting a relatively short SMS messages (e.g., less than about 200 characters), if several mobile stations were simultaneously transmitting longer SMS messages the overall system capacity can be reduced.
Furthermore, existing Teleservices place restrictions on the length of messages that can be transmitted from a mobile station using the R-DATA message. Such restrictions can be a significant disadvantage when it is desired to transmit a message that exceeds the specified maximum length of the R-DATA message for a particular system.
More particularly, and referring specifically to the IS-136 air interface, Teleservices are supported for SMS and Over the Air Service Provisioning, that is, Over-the-Air Activation Teleservices (OATS). Other Teleservices are envisioned in the future. These Teleservices utilize the Layer 3 R-DATA message to transport their transactions over the air interface. At the BMI the R-DATA message is translated into a Short Message Delivery Point-to-Point (SMDPP) message for relay through the IS-41 network. These two mechanisms (R-DATA and SMDPP) can each impose constraints on the size of a Teleservice or Application transaction. It would thus be desirable to provide a method to free the Teleservice definition from these arbitrary constraints. In fact, these constraints may be so onerous that they may effectively shut a particular Teleservice down.
In IS-136 the BMI may limit the size of R-DATA messages through the R.sub.-- Data.sub.-- Message Length information element provided in the Fast Broadcast Control Channel (F-BCCH) Access Parameters message. This currently allows the BMI to limit mobile station originated R-DATA messages to either 31, 63, 127, or "Limited only by layer 2 format" (which provides approximately 250) bytes in length. There is also a proposal to define a new value that provides an air interface limit that conforms to the largest user data space that may be accommodated into one IS-41 SMDPP message. This is currently expected to be approximately 204 bytes.